1. Technical Field
The present invention relates to a technique of controlling viewing angle characteristics of a liquid crystal display, and more particularly to an information processing apparatus, a method of controlling a display of a liquid crystal display, and a program for executing the method of controlling the display that provide a narrow viewing angle characteristic by controlling gradation of the liquid crystal display.
2. Description of Related Art
A liquid crystal display is used for an information processing apparatus, such as a laptop computer, a notebook computer, a PDA, and a mobile phone in many cases to thereby provide a display to a user. Particularly, in recent years, due to downsizing of the information processing apparatus, the information processing apparatus is increasingly used under a situation where persons other than the user are present within easy reach. Especially, information displayed on the liquid crystal display of a portable information processing apparatus includes privacy information in many cases, and therefore preferably the persons other than the user are prevented from being able to recognize the information.
Various kinds of methods for controlling a viewing angle in the liquid crystal display have been disclosed so far. For example, in Japanese Unexamined Patent Publication (Kokai) No. 2003-295160, there is disclosed a liquid crystal display in which high contrast is provided even in a wide viewing angle by adjusting distortion due to a viewing angle of a gradation curve on a display screen, and on the contrary, by providing a display image with an narrow viewing angle, information that user does not want to be seen by others is displayed. In Japanese Unexamined Patent Publication (Kokai) No. 2003-131230, there is disclosed a display unit that obtains a narrow viewing angle characteristic by using a prism sheet almost meeting with an optical property in a viewing angle being narrowed. Moreover, in Japanese Unexamined Patent Publication (Kokai) No. 2004-318112, there is disclosed a liquid crystal display provided with a look-up table for controlling a driving voltage supplied to a liquid crystal panel for the purpose of providing a narrow viewing angle. Furthermore, in Rocket_SecurityShades, there is employed a method of controlling the viewing angle, in which a display gradation range is narrowed by not using gradation levels at both sides of higher gradation levels and lower gradation levels for the display, to thereby reduce visibility with respect to a large viewing angle.
According to the method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2003-295160, in order to adjust the distortion due to the viewing angle of the gradation curve, there is employed the method, in which a plurality of look-up tables to be referenced are prepared, and one pixel is further divided into a plurality of sub-pixels to thereby provide different gradation curves to respective sub-pixels. For this reason, according to the method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2003-295160, there has been such inconvenience that a configuration of a liquid crystal display panel has needed to be changed significantly, and in addition to that, contrast characteristics with respect to the viewing angle might not be necessarily controlled sufficiently.
Meanwhile, according to achieving the narrow viewing angle using the prism sheet described in Japanese Unexamined Patent Publication (Kokai) No. 2003-131230, a configuration of an LCD panel needs to be changed, for example, by preparing the prism sheets with different dimensions or the like for respective LCD panels. Additionally, in the liquid crystal display for controlling the driving voltage of the LCD to provide the narrow viewing angle disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2004-318112, in attempting to achieve the narrow viewing angle, there is employed the method of generating a gradation collapse in a diagonal viewing angle by increasing the driving voltage on a low gradation side. According to the method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2004-318112, in order to control the driving of the liquid crystal display, it is necessary to change the driving voltage of the LCD panel, so that there is such an inconvenience that flexibility to the liquid crystal display cannot be obtained, for example a dedicated driver for LCD is required.
Furthermore, also in the conventional art described in Rocket_SecurityShades, since the narrow viewing angle has been achieved by only reducing a gradation width to be displayed, contrast has wholly been decreased, so that there has been such an inconvenience that contrast at the time of being seen from the front has been decreased. Additionally, according to the method described in Rocket_SecurityShades, even when the LCD panel is seen from the large viewing angle, a displayed image will be visible to some extent, so that there is such an inconvenience that good privacy protection cannot necessarily be provided to the user.
Other than this, in order to narrow the viewing angle, there has been employed a method of pasting a film formed into a louver structure, the so-called privacy filter on the liquid crystal display panel or the like. However, this causes other problems, in that the user needs to purchase the privacy filter, mounting the privacy filter has been troublesome, the viewing angle has not been dynamically controllable in response to a user's request, brightness has been reduced, a film exchange has been required because of durability of the film, or the like, so that the method has not been able to provide sufficient visibility and permanency.